Air carrier (4)
I believe the answer is:
hose
'air carrier' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hose that I've seen before include "Piping" , "Stockings; drench" , "footwear" , "One with doublet; a tube" , "Breeches (worn with a doublet)" .)